1. Field of the Invention
This invention relates to the field of valves for draining tanks and sumps quickly and easily. In particular, it relates to quick-drain valves that can be locked in the open position for unattended draining.
2. The Prior Art
One type of drain valve is used to check the fuel in the tanks of an aircraft to be sure that it is not contaminated by water. Such valves have springs that keep them normally closed fluid-tight to prevent any leakage at all except when the valve is deliberately opened to allow a small quantity of the fluid to flow out, usually into a transparent container. It is customary to hold the small container to the light to see if any water has condensed in the tank and settled to the bottom. If it has, the valve may be held open a short additional time to allow all of the condensed water to drain out, but it is important that, once the person making the check has finished doing so, the spring loading in the valve return the valve to its shutoff condition without fail. Since a detent that would hold the valve in the open position until the valve was deliberately shut off could make it easy for the valve to be accidentally left open, thereby draining the tank of all fuel, detents are specifically not included in such valves. One example of such a valve is shown in U.S. Pat. No. 3,198,016 to Poorman and another is shown in U.S. Pat. No. 2,506,722 to Kuehn et al.
A similar valve is shown in U.S. Pat. No. 2,577,654 to Gates and is used to vent air from hot water radiators. As in the case of aircraft fuel-checking valves, it important that the venting valve of Gates return to its closed condition as soon as pressure is released, and, thus, no detent is provided.
U.S. Pat. No. 2,690,895 to Barcus provides a spring retention device, but Barcus does not suggest a groove extending longitudinally along the body of his valve and having a laterally offset portion at the end of the groove to provide a positive lock to hold the valve in the open position. Instead, he uses an annular groove engaged by spring fingers which are attached to the valve stem and merely press inwardly along a sloping surface to hold his valve open. The spring that urges the stem of his valve to the closed position continuously exerts longitudinal pressure that tends to overcome the holding force of the spring fingers and return the valve to the closed position, which makes the valve too prone to premature closure.
Szitar, Jr. depends on having four balls move in a radial direction in response to the combined pressure of opposing forces developed between sloping surfaces and a radial surface to lock and unlock his valve stem so that it can move longitudinally to open and close his valve in U.S. Pat. No. 2,692.112. In addition, the end of his stem extends radially out too far to fit into the passage through the body of the valve to allow the stem to be replaced because of wear.
Laipply et al. show a drain valve in U.S. Pat. No. 4,745,894 that requires an additional sleeve outside the body of the valve to cooperate with a ball that moves radially to release the lock and allow the stem to move to a position in which the valve is open.